In recent years, plastic products are being substituted for glass products from the viewpoints of moldability and a reduction in weight. Since, however, the surface of the plastic products is likely to be scratched, a hardcoat film is in many cases applied to the plastic products to impart scratch resistance. Also in the case of the conventional glass products, there is a growing tendency for a plastic film to be applied thereto to prevent scattering. Due to unsatisfactory hardness of the plastic films, however, a hardcoat is in most cases formed on the surface of the plastic films.
The conventional hardcoat film has been produced by coating the surface of a plastic substrate film with a highly scratch-resistant resin, generally a thermosetting resin or an ionizing radiation curing resin, such as an ultraviolet curing resin, either directly or through an about 1 μm-thick primer layer to a small thickness of about 3 to 15 μm (for example, Japanese Patent Laid-Open No. 151914/1995).
Further, in the conventional hardcoat films, an attempt has been made to add an inorganic filler to a film-forming organic component having a polymerizable functional group to enhance the hardness (for example, Japanese Patent Laid-Open No. 41362/1990).
The conventional hardcoats, however, have a small coating thickness and, hence, hardcoat is directly influenced by the deformation of the plastic substrate film underlying the hardcoat. That is, the surface strength is low and unsatisfactory.
On the other hand, merely increasing the thickness of the hardcoat to a larger value than the conventional thickness, that is, more than 3 to 15 μm, can improve the surface hardness of the hardcoat film, but on the other hand, cracking or peeling is likely to occur and, at the same time, curling derived from cure shrinkage is increased. Therefore, the hardcoat film cannot be put to practical use.
In the conventional hardcoat films, incorporation of the inorganic filler into the organic component having a polymerizable functional group can provide a film having improved surface hardness. In this case, however, cracking and peeling are likely to occur and, at the same time, curling derived from cure shrinkage is increased. This renders the hardcoat film unsatisfactory for practical use.
When the hardcoats are used as protective films for preventing specific products from being scratched, production numbers, dates and the like associated with the product are printed on the hardcoats. In this case, for hardcoats to which scratch resistance has been imparted, for example, by forming a dense film as the surface layer or by imparting slipperiness to the surface, a printing ink is less likely to be penetrated thereinto or a dye for sublimation transfer is less likely to be fixed. This structure results in poor productivity.
When a tacky layer is present on the backside of the plastic substrate film, the formation of a hardcoat on the other side of the substrate film followed by superposition or winding of the assemblies poses a problem that the tacky layer is transferred to the hardcoat.